#pragma once

#ifndef _TRITON_TOOLS_THREAD_POOL_H_
#define _TRITON_TOOLS_THREAD_POOL_H_

#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>

class ThreadPool {
public:
    ThreadPool(size_t threads)
        :   stop(false) {
      for(size_t i = 0;i < threads;++i)
          workers.emplace_back(
              [this] {
                for(;;){
                  std::function<void()> task;
                  {
                    std::unique_lock<std::mutex> lock(this->queue_mutex);
                    this->condition.wait(lock,
                      [this]{ return this->stop || !this->tasks.empty(); });
                    if(this->stop && this->tasks.empty())
                      return;
                    task = std::move(this->tasks.front());
                    this->tasks.pop();
                  }
                  task();
                }
              }
          );
    }


    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args)
        -> std::future<typename std::result_of<F(Args...)>::type>
    {
        using return_type = typename std::result_of<F(Args...)>::type;

        auto task = std::make_shared< std::packaged_task<return_type()> >(
                std::bind(std::forward<F>(f), std::forward<Args>(args)...)
            );

        std::future<return_type> res = task->get_future();
        {
            std::unique_lock<std::mutex> lock(queue_mutex);

            // don't allow enqueueing after stopping the pool
            if(stop)
                throw std::runtime_error("enqueue on stopped ThreadPool");

            tasks.emplace([task](){ (*task)(); });
        }
        condition.notify_one();
        return res;
    }


    ~ThreadPool() {
        {
          std::unique_lock<std::mutex> lock(queue_mutex);
          stop = true;
        }
        condition.notify_all();
        for(std::thread &worker: workers)
          worker.join();
    }


private:
    // need to keep track of threads so we can join them
    std::vector< std::thread > workers;
    // the task queue
    std::queue< std::function<void()> > tasks;

    // synchronization
    std::mutex queue_mutex;
    std::condition_variable condition;
    bool stop;
};


#endif
